GL-4 and GL-5 gear oil?

[DayBreak]

For the past 6 years, I have been using marine Quicksilver/Mercury SAE 90 Gear Lube for my annual lower unit gear oil changes. I recently noticed that this oil is rated GL-4. The manufacturer states that this oil is good for all outboard motor lower units. Today, I noticed that the Suzuki Marine ECSTAR SAE 90 Hypoid Gear Oil has a rating of GL-5. I cannot find in my owner's manual or anywhere on-line if my 2017 Suzuki DF-140 outboard should use a GL-5 rated oil. Should I switch back to the OEM Suzuki GL-5 gear oil or can I stay with the marine Mercury GL-4 oil? Thanks. Gary

[thataway]

The way most of us run our C Dory's the GL 4 is probably adequate. Suzuki went to GL5 in about 2015. GL 5 should not be used in earlier motors. The GL5 has more protective elements and a slightly higher visocity.

[DayBreak]

Thank you Bob. I will switch back to the Suzuki GL-5 gear oil. I have read that GL-5 has twice the amount of sulfur and phosphorous when compared to GL-4. The sulfur is corrosive to copper, brass and bronze (yellow metals) and that is why it is not recommended in earlier motors.